(137b) Experimental and Modeling Studies of Reactive Distillation

Reactive and catalytic distillation combine reaction and separation in a single equipment and are becoming increasingly important in the context of process intensification, energy management and pollution prevention. Such operations offer a number of advantages such as (i) reduction in capital costs, (ii) reduced recycle due to the overcoming the thermodynamic equilibrium barrier due to in-situ product removal, (iii) reduction of heat duty by efficient use of heat of reaction. Proper design of these systems require both the steady state model and a dynamic model for control purposes. The theme of this talk is to provide an overview of some application areas and present steady state and dynamic models developed at CREL in Washington University at St. Louis. In addition some experimental results on a novel application, photochemical reactive distillation, will also be reviewed.

For steady state simulation, it was observed that the general rate based models are preferable than the equilibrium stage based models since the Murphee efficiency is a difficult parameter to predict a priori. Computational efficiency of the rate based model was improved by constructing a robust algorithm based on homotopy continuation methods. The results were applied to investigate the parametric sensitivity and energy management aspects of reactive distillation.

For dynamic simulation, implicit Euler method (for time derivatives) combined with homotopy methods (for reaction non-linearity) was found to be suitable. Although the implicit Euler requires smaller time steps it is unconditionally stable thereby leading to a robust algorithm. The results were applied to ethyl acetate production by reactive distillation. A number of interesting features were found in the dynamic simulation. These include the rapid changes in the calculated ?tray efficiencies?, a wave type dynamics, unfavorable operating situations during start-up resulting in a narrower window of design as compared to the design based on steady state situation. The computational algorithm and the results have obvious implications in the control and start up of reactive distillation processes.

Potential applications to newer areas are also being analyzed and some examples will also be presented in this lecture. A novel example is the combination of photochemical reaction with reactive distillation. The experimental results for chlorination of toluene indicates that a 96% selectivity to benzyl chloride, the first chlorinated product, could be obtained at a toluene conversion of 78%. The results are encouraging and indicates the commercial potential. Other applications can be found in the areas of unit processes such as oxidation, reductive amination, etc., which have direct impact in ?Green? processing. These are briefly reviewed in the presentation and the Green processing impact of this technology is indicated.